Investigations on the fundamental chemical and structural aspects of heparin and heparan sulfate will be continued. Such studies will contribute to the elucidation of the relationship between chemical structure and biologic activity of these substances. Furthermore, the confusion regarding clinical effectiveness, often prevalent in the application of heparin preparations from different sources, may be clarified by an understanding of structural details, as well as by an assessment of purity and contaminating substances present in clinically used preparations. As a practical application of the studies on heparin, modified products of this mucopolysaccharide will be utilized for determining the effect of various parameters on absorption from the digestive tract of rhesus monkeys and on the determination of the efficacy of these preparations in the inhibition of atheromatous plaque formation in rabbits and rhesus monkeys. Heparin isolated from human lung tissue is being characterized for comparison with heparins of animal sources which are used for clinical purposes. This information is considered of value for assessment of characteristics of heparins which are desirable for human applications.